Treatment of materials



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TREATMENT o1 MATERIALS Jan, 13, 1959 2v sheets-sheet 1 Filed March 7, 1958 v RMR.

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n SESS@ Jan. 13, 1959 H. A. DEPEW ET AL 2,868,673

TREATMENT 0F MATERIALS 2 .Sheets-Sheet 2 Filed March '7, 1958 2,868,673 TREATMENT oF MATERIALS Harlan A. Depew, Glendale, Patrick D. Quinn, St. Louis, and George R. Waitkins, Des Peres,'Mo., assignors to American Zinc, Lead & Smelting Company, St. Louis,

Mo., a corporation of Maine Application March 7, 1958, Serial'No. 19,916

20 Claims. Cl. 117-137) This invention relates to the treatment of fibrous and porous materials. It has particular application to the treatment of wood and fabric, to render those materials resistant to fire and to the attacks of microorganisms. The term fabric is usedherein to indicate fibrous sheet materials which may be woven, knitted, felted, laid, or otherwise formed, and to fibers, which may be in the form of yarn, thread, fur, hair, short pieces of stock or the like, which are used to produce these sheet materials. Thus, the term fabric includes cloth, (whether of animal liber, e. g., wool, silk; vegetable liber, e. g., cotton, linen; mineral fiber, e. g., asbestos; or synthetic ber, e. g., rayon, nylon) and paper.

While this invention is not limited thereto, it has particular application to cellulosic materials such asl wood, and hers, natural and regenerated.

This application isy a continuation as to common sub1 i ject matter, of applications Serial Nos. 523,383 and 523,386, now abandoned, both'led July 20, 1955.

. The need for permanentlylire resistant wood is well`v recognized. lThe fire code of some cities requires tire resistant treatment of wood used for the interior of buildings, and methods of treatment have been devised which meet these requirements. However, the wood treating processes commonly used heretofore have not produced wood suitable for exterior use, and no commercially accepted method for producing such wood has been developed, in spite of the fact that there is apressing need for a lire resistant wood for use in ships, railroad trestles, and the exteriors of buildings of all sorts.

One of the materials used heretofore, which renders wood tire resistant and in addition toxic to fungi and 'termites' and yet is non-toxic to warm-blooded animals,

Zinc chloride has, however, several It is readily leached is zinc chloride. important undesirable properties.

from wood by water. To render wood tire resistant by` its use, around four pounds per cubic foot of zinc chloride are required, and when this amount is put into wood, it makes the wood hygroscopic. In humid atmospheres,

the water pick up is large. Under these conditions, the

zinc chloride dissociates, producing hydrochloric acid that damages the wood severely, so that after a few years the wood has little strength.

Chromates have been added to the fzinc chloride in order to make the zinc chloride less corrosive in the treating equipment, and it has been claimed that the addition of the chromates increased the insolubility of the Zinc but the evidence does not substantiate the claim.

Since chromium will catalyze combustion, some borc acid and ammonium sulfate are added to the chromated zinc chloride in what is known commercially as the CZC-FR (Fire Resistant) grade, but commercial exe perience has not justified this composition for wood forv exterior service.

A more positive approach to this problem waslpresented by Ferguson, U. S. Patent No. 1,261,736; Arent, U.`S. Patent No. 1,318,524; and Munroe, U. S. Patent' No.f.1,338,322. They dissolved zinc chloride ora mixv 2,368,673 e Patented Jan. 13, 1959 2 ture of zinc chloride and zinc phosphate in ammonium vhydroxide and impregnated the wood with this composition. Then when the ammonia was evaporated they reported the presence of zinc hydroxide and basic compounds that were'somewhat insoluble.

We have investigated the methods of Ferguson, Arent and Munroe. ln our tests of those methods, zinc chloride was dissolve-d in aqua ammonia to form a solution containing 14% Zn and 15.7% Cl. Wood was impregnated with the solution and then dried. Fire tube tests on the leached wood showed that around 8 lbs. of zine, calculated as ZnO, per cubic foot of wood were required to give tive tube results below 30%.

The performance is satisfactory but the amounts of zinc required are -too great to be economically feasible.

In these tests and the tests set out hereafter in connection with the illustrative examples 0f the process of our invention as applied to wood, the tire tube losses are -determined in accordance with ASTM E-69-50- )ASTM Standards 1952, part 4, p. 1014. Briey, in these 'fre ltube tests, a test stick of wood of-standard dimensions is suspended vertically within a metal tube or ue,

from the beam of a balance which is calibrated in terms of percentl of weight of the test stick, rather than in absolute units. Thatis, the scale of the balance runs from 0% when a stan-dard stick is initially put in place, to 100% when no stick Vis present. A llame of standard size and intensity is applied to thev lower end of the sus-.

pended stick. As the stick is consumed by the flame, the percentage loss of weight is indicated directly by a pointer on the balance. This percentage loss is recorded at half minute intervals for four minutes when the applied flame is withdrawn and then continued until the loss of weight for a one minute period does not exceed 1%. Untreated Wood will burn to 75-85% loss in less than three minutes. The marginal loss is approximately 40% after four minutes. If more than 40% loss is sustained, the entire stick will be charred. 40% loss is sustained, the llame becomes self-extinguishing and a portion of the stick remains uncharted. A

vance in the Wood treating art over Ferguson, Arent and Munroe. The Pershall process involves preparing basic zinc chloride, dissolving it in aqueous ammonia, and treating wood with the solution. Nevertheless, the Pershall process has several shortcomings. The zinc concen- .ltration of the saturated solution is only about 10%, so

that it is difcult with many woods to put enough zincy in the wood with one impregnation to give the desired tire resistance. The solution is unstable. On standing, the zinc oxide polymer produced when the basic zinc chloride is dissolved in ammonia breaks down and deposits zinc hydroxide crystals on the walls of the treating container. The deposit in the wood is not uniform. On evaporation of the ammonia, the first precipitate is zinc oxide or zinc hydroxide because of the highly basic nature of the solution. Then very basic zinc `chlorides-are .p precipitated, followed by less basic zincv chlorides; then If less than 3 zinc diamino chloride (ZnClz'ZNI-Ia), and finally, soluble NH4C1. The high pH of the alkaline solution may damage the wood. The adsorbed ammonia tends to increase the chlorine so-lubility. The presence of ammonium chloride in thewood is not desirable f-or reasons which. are outlined hereafter in connection with Example l. v

The impregnation of various-fabrics with salts to render them re resistant, mildew resistant, opaque, or to achieve various other results, is broadly old. Temporary lire resistance has been given by treating v cloth with ammonium phosphate, ammonium sulfarnate or zinc chloride, but these materials are water soluble and are'removed by rinsing. Various phosphorous, chlorine, urea, and resin treatments have been recommended, but the treated cloth has not been sufficiently flame resistant for lthe purposes 'to which the `fabrics of this invention may be put.

Another treatment that has had commercial success consists of impregnating cloth with a highly acidic solution of titanium and antimony chlorides. After certain intermediate treatment, the acid in the cloth is neutralized with a solution of an alkali such as sodium carbonate. Unfortunately, the acidity vof the solution and its tendency to damage the cloth and to corrode the treating equipment limits the usefulness of this treating process. Furthermore, the treated cloth is expensive and may irritate the skin.

It would-appear that 'the teachings of the United States patents to Ferguson, No. 1,261,736; Arent, No. 1,318,524; Munroe, No. V1,338,322 and Pershall, No. 2,637,691, all of which apply to the treatment of wood, might be applied tothe treatment of fabric.y However, the application `of the processes of those references to cloth has produced disappointing results. `The ammoniacal solutions required in those processes tend to injure the fabricpthe salts are deposited loosely on the surface of the fabric so that they wash out easily,'a'nd'th'e 'fabric dusts badly.

vIt yhas even beensu'ggestedto deposit 'salts of triand tetralvalent `metals 'in substrates Vby 'means of alkylene oxides, but the 'dival'ent zinc has ybeen considered 'too reactive, a suitable process for its use has not 'heretofore been devised, and the peculiar virtues of its use have remained undiscovered heretofore.

We investigated a process of first treating fabric with zinc chloride and then immersing the impregnated cloth in an alkalinesolution in an attempt to `deposit basic zinc chloride in the cloth, but' this proces-s yhas proved unsatisfactory. The salts are largely deposited in the liquid and between the bers of the "fabric so that upon being rinsed, the fabric loses its desirable properties. n

One of the objectsof this invention is to provide a simple, economical, Veffective process for treating porous and fibrous materials to impregnate them with a basic zinc salt, in such a way vthat 4the basic zinc .salt is stable and water-insoluble, and resists displacement.

Another object is to Vprovide treated materials which are tire resistant, resistant to the attacks of vmicro-organisms, termites, and the like, which are resistant to the deteriorating effect of acidic materials, and which are Vnonhygroscopic and nearly neutral.

In the case of wood, another object is to pro-vide a process which may be used to produce Wood of low electrical conductivity, which is readily worked with high "speed tools, and is paintable.

Other objects Will become 'apparent to those skilled in the art in the light of the `following description and laccompanying drawing.

Inthe drawing, Fig. l is a flow diagram of one illustrative embodiment of the process of this invention applied to wood; and Fig. 2 is a 'ow diagram of one illustrative embodiment of the process 'of this 'invention applied to fabric` In accordance wth'this invention generally stared, 'a process i's 'provided by which a basic zines/alt is vformed and deposited in place within the pores of porous material, and in and on the surface of bers of fibrous materials.

The term basic zinc salt is used herein to describe a co-precipitate of zinc hydroxide with a normally Water soluble zinc salt. The formula for such a salt may be represented as ZnAn.nZn(OH)2,vin which An is the anion of a water soluble Zinc salt and n is a number, the size of which indicates the'basicity'of the material. The basicity (n) is preferably in `theneighborhood of 2 to 3, a1- 'though it may, for certain applicationspvary ,'fromone quarter to or seven or more. The pH ofthe basic zinc salt is lessv than eight, andi-t1 Athe preferred range Aof basicities, is about 6.l

The process of this invention is a two-step process, wherein the poresof Wood or the Llike lor the bers of fabric or the like are lirst impregnated with one reactant, and subsequently impregnated with a second reactant, in such a way as to cause,`upon the introduction ofthe second reactant, an initial formation ofzinc hydroxide and the subsequent coprecipitation of zinc hydroxide and a water-soluble zinc salt, as a water-insoluble basic zinc salt, in situ.l

lnl treating either `wood or fabric, the material to be treated may first be impregnated with a solution vof water solublerzinc salt. The solution may be eitheran aqueous solution or a ysolution'of water soluble zinc salt in `an organic y.solvent such as alcohol.y The excess solution is then preferably removed, andthe material is subsequently impregnated with a basic material lin an'amount suicient to react with the water soluble zinc salt'to `produce zinc hydroxide, under such conditions as to` permit the zinc hydroxide then to combine with the residual water-soluble zincsalt, to form the basic zinc salt.

The term basic material is use d herein to inc`:lude alkylene oxides which are acid acceptors, such as ethylene oxide, as well as such bases ,as ammoniumhydroxide,V

sodium hydroxide, barium hydroxide, ethanol amines 'and the like. It also includes mixtures of various bases and of bases and 'acid acceptors. 'It"iricludes'aqueous and organic solutions of bases and of acid acceptors, .and they gaseous forms of such acceptors and basesv as' ethylene oxide and ammonia. It alsoincludes solutions of'bases in which zinc salts are dissolved. y v

In the treatment of fabric, it is necessary thatl the water soluble zinc salt be added rst, and the reactant which produces the zinc hydroxide be added second, and that the basic material be introduced in a medium by whichv the zinc salt is not leached or dislodged. To this end, the basic material may be introduced as a gas, such as ammonia or an amine of the character of monomethylamine, or a gaseous alkylene oxide, such as ethylene oxide, vaporized propylene oxide, v cpic'hlorhydrin, mixed butylene oxides, arylalkyl oxides, cyclo-alkyl oxides and polyepoxy compounds, o1' inthe form Lof a solution of basic material in an organic solventin which the Watersoluble zinc salt is insoluble.

In the treatment of wood, the wood may first bel irn-V pregnated with the basic material, and thengwith `the water soluble salt, and such a procedure has certain advan-tages. In the case of a porous -material such as wood, the dislodgrnent of the frstjsolution is' Y'not as much la problem as in the casev of thefabric, because the pores serve as little cells, in which ther'eaction can take place. Thus, the basic materials can include water solutions of ammonium hydroxide, sodium hydroxide, barium hydroxide, andthe like, as well as the basicmaterials listed in connection with the impregnation of fabric.

The precipitated basic Zinc salt in the case of fibrous material, is deposited in andk on the surface of the fibers in such a Way as to strongly resist dislodgment by wash- 4Of the watersoluble .zinc salts, zinc chlorideyis pre1,

aseaevs i this invention to impart to the fabric such characteristics as softness or a starchy character, water repellance or the like. For example, hydroxyethylcellulose may be dissolved in a zinc chloride solution and will be deposited with the basic zinc chloride when it is precipitated. Itgives the cloth a starchy, smooth feel, with increased wash resistance. Examples of other materials which can be dissolved in the zinc chloride solution and which are insolubilized with the deposition of the zinc are polyacrylonitrile and cellulose acetate. An alkyl diketene such as Hercules Aquapel may be added to the treating solution kas an emulsion, and polyacrylamide can be dissolved in the solution. y

In carrying out the process of this invention, as applied to porous materials of which wood will be taken as the example, the wood may be impregnated by pressure or by diffusion. Two general procedures for pressure impregnation of wood are now used. These are what will be referred `to hereafter as'the empty cell and full cell procedures, respectively.

In the empty cell procedure, the wood is placed in a pressure vessel, commonly a horizontal cylinder, and moderate air pressure is applied. An impregnant solutionis then forced into the cylinder and into the Wood.

Pressure of up to 100-150 pounds per square inch gauge is applied, forcing the impregnant solution deep into the wood. The pressure is then released and -the-unabsorbed solution is removed from the cylinder. A vacuum is then applied and the residual air in the capillaries of the wood expands, thereby forcing the excess liquid in the pores from the wood. The wood pores are thus covered with a thin film of impregnant. In the two step process of this invention, a considerable volume of open pores is thereby provided for the reception of the second solution.

In the full cell procedure, a high vacuum is applied initially to the pressure vessel containing the wood. An impregnating solution is added to the cylinder and surrounds the Wood While the Vacuum is maintained. Positive pressure is then applied yto force the impregnant into the wood. At the end of the impregnation, the pressure is released. A final vacuum is applied, and the unabsorbed solution is removed from the cylinder. Since the residual air was -to a large extent removed from the pores by the initial vacuum, a considerable amount of liquid remains in the pores. However, of the relatively small amount of residual' air which was not removed from the pores of the wood by the initial vacuum, some dissolves in the solution during the pressure period. When the pressure is released, this dissolved air comes out of solution in the form of bubbles, causing the wood to bleed. The application'of the final vacuum prevents or'minimizes bleeding by rapidly removing the solution that would normally run out anywayv by virtue of the expansion of the dissolved sure determines the amount of residual air in the capil-N 6 laris and thu's is` a means for regulating the ai'n'unt of impregnant solution which remains in the pores.

Many modifications of the operating procedures are` possible but in general, the wood is partly filled with the first solution and is then more completely filled with the second solution.

If time is no object, it is unnecessary to use pressure, A

but diffusion alone may be relied upon. The woo'd can be fastened down in an opentank containing. the firstv solution. Over a period of time, the air in the pores is displaced by the liquid. `The' solution is then drawn 0E and the second solution is added. The chemicals of the second solution diffuse into the wood to react with the chemicals of the first solution to form and deposit waterinsoluble basic zinc salts in the wood.

When the diffusion procedure is chosen, the time required will depend upon the size of the piece of wood. Combinations of full or empty cell procedues and the diffusion procedure may also be used. For example, the

pores of the wood may be filled by the full cell process with the first solution. The wood may then be immersed in the second solution to permit the chemicals of thesecond solution to diffuse into the wood and react with' the chemicals of the first solution to form and precipitate the basic zinc salts in the wood.

The following eight examples are illustrative of the n process of this invention as applied to wood.

EXAMPLE I tional freesolution is withdrawn from the tank.

An aqueous solution of sodium hydroxide and ammonia, containing 4.7% NaOH, 7.8% NH3 and the balance water, is then introduced into the pressure tank while the vacuumis maintained. An air pressure of approximately p. s. i. g. is then 'applied to the basic solution for one hour. The pressure is then released and the unabsorbed solution removed from the cylinder. A vacuum of about 22 inches gauge is`applied to remove from the pores any solution which is likely to cause bleeding.

The entire process is carried out at room temperature.

The results are indicated in the following table. The retention of zinc was measured as the difference between the amount of solution introduced into the pressure tank and the amount of unretained solution withdrawn. The actual retention was less, b ecause the residual drawn-off NaOH--NH3 solution contained 1% of zinc.

Percent Fire Tube Losses After 15 Days Leaching Retention, Lbs/Cu. Ft. as ZnO ASTM Final 3 Min.

ying of the wood, and dissolve zinc 'compounds during leaching. These objections are less applicable to sodium chloride, which is produced when sodium hydroxide is Sufficient of a 3,3% water solution of zincA Air pressure of approximately 125 pfs. i. g. is then applied to the solution within the tank for one hour. The pressure is then released and the unabsorbed solution withdrawn from the tank. A vacuum of about 22'? inches gauge is applied for 5-10 minutes,'and any addi-4 used. However, the use of sodium hydroxide increases the pH of the treatingl solution. A mixture of sodium andi ammonium hydroxide is, therefore, preferred over a solution of only sodium hydroxide. The use of a strong organic base such as the ethanol amines or their equivalents in place of the sodium hydroxide ismore expensive, but technicallyI superior.

A zinc sulfate solution can be used inA place of the zine chloride solution in the processof Example I. To obtain a solution of ZnSOyHZO of the same concentration of zinc as. the zinc chloride solution, it is necessary to raise the temperature to. 50'-60 C. to hold the zinc sulfate in solution. Otherwise, the process may be the same. When zinc sulfate is used in place of zinc chloride, the resultant wood has 10'%-15`% greater re loss, but the resultant wood is of better color and holds paint even better than the zinc chloride treated wood.

Mixtures of half zinc chloride and halfzinc sulfate give intermediate results.

EXAMPLE II Twenty'teststicks, divided` into groups of ten, are im? pregnated at room temperature with zinc chloride solution by the, full 'cell.method, the solution being kept under a pressure of about 125 p. s. i. g. for one hour. They unabsorbed impregnant solution is withdrawn from the pressure tank; A vacuum of about 22 inches gauge is applied, and one pound of ethylene oxide gas is admitted to the treating cylinder while the vacuum is main-V tained'. One pound of ethylene oxide is 140% of the theoretical amount required to form ZnO or Zn(OH)2 with. theretained zinc chloride, based on the following equation:

2(CH2)'2O`}VZnCI`2-}2H2O`=Zn.(OH)`2-lZCHZCHQOHCl Owing to the expansion. and consequent displacement of impregnant liquid from the pores of the. wood during itsv absorption of the; ethylene oxide. gas, the wetV sticks4 sus.- tain a Weight loss, as` shown. in the. following table:

The following table. shows the results obtained by this process:

Wt. 211013 Wt. ZnCl Zine Cal- Final Group Added, Corrected eulated Days Fire Lbs./ for Loss as ZnO Leach Tube Gu. Ft. Loss 1 8.1 i 7.1 4.1 0 30 2 as I 7;? 4.4 15 33 Air drying the sticks for lr6 hours between the two stages, i. e., between the zinc chloride impregnation and ethylene oxide addition, practically eliminates the salt loss due to the expansion of the zinc chloride solution during gas absorption. The empty cell process may advan-tageously be used for the zinc chloride impregnation. The ethylene oxide can then be added as a Water solution. Since ethylene oxide and water are miscible, an amount of ethylene oxide equal to about 140% ofthe theoretical requirements as set outabove may be used with an amount of water suilicient to immerse the wood. -lt will be noted that in spite of the 40% excess of ethylene oxide in Example l-I, the. zinc chloride is not converted completely tozinc hydroxide, but rather forms basic zinc chloride. 1t is believed that as the zinc hydroxide is formed,'it

combines with unreacted zinc chloride to precipitate basic zinc chloride which does not react with theethylene' oxide. The amount of the excess of ethylene oxide will` determine thebasicity of the; basic zinc chloride, i. e., the proportion of zinohydroxide to zinc chloride. in the basic zinc chloride. The complete reactionis as follows:

Ammonia gas maybe usedin place of the ethylene oxide. slowly, because the; heat of Solution and; ofv reaction and thev lowered: specific:v gravity of the zinc chloride solution.v

inthe wood as the ammonia gas entersl thev solution tendto cause bleeding of thesolution before thebasic, zincv chloride is formed. The; tendencyl to bleedcan be. re-

duced by adding the zinc chloride by the empty cellk process. and partially drying the wood after it is impreg.- nated with the'k zinc salt. and before the ammonia is."

added. Y

'll'herev are several advantages in the use of alkyleneoxides. such. asl ethylene oxide over the-use of ammonia.

The wood doesnotbecome alkaor other similar bases. line. This is true whether the alkylene oxide is introduced as a gas or in water. solution.

An additional? important advantage, of the. use of analkylene oXide-.arisesfrom the fact that the. chlorhydrin.

produced isnon-ionic, i. e., electrically non-conductive and volatile.. This permits; the wood to be made of lowv electrical conductance. In order to obtain the lowest electrical conductance, the untreated wood may be leached with water to removeiwater-soluble; salts originally in thev wood; dried; impregnatedv with zinc chloride solution;4

and. treated with an; alkylene oxide, either in water solutio-n or as a gas.. lf desired, it can be dried in. a kiln to evaporate anyexcess of the alkylene oxide and ltsreaction products, e. g., chlorhydrin. The kiln-treated wood.

will contain. practically pure basic: zincA chloride. The.

wood so ytreated is of. low electrical conductance owing.

to the. absence of water-soluble salts. It has improved dimensional stability;

While ethylene oxide has been used as an example.

of a suitable. alkylene oxide, .other alkylene oxides, such as propyleneoxide, butylene oxide, epichlorhydrin and styrene oxide may be used. Styrene oxide is less satisfactory than the rest because it is less soluble in waterv and has a higher boiling point.

EXAMPLE III Test sticks areV impregnated .with a 33% water soln. tion of Zinc. chloride by the empty cell procedure as in Example l, and then with4 a water solution of ammoniacal basic zinc chloride, analyzing 9.3%A Zn, 3.9% Cl, and 19.7% NH3, by the full cell procedure asin Example l.

Retention Calculated as Percent Fire Tube Lbs. ZnO per Cubic Actual Loss After l5 Days Foot of Wood Based onA Retention Leaching Weight Taken' Up Total Based on Analysis. of Wood From` ZnCh From Am. f 3 Mln. ASTM.

Basic ZnGlz Final It is evident from columns 3 and 4 that zinc chloride is extracted during the limpregnation with the ammoniacal solution. After l5 days leaching the wood contains 4.5 lbs. ZnO per cubic foot of wood and 0.9 lb. chlorine per cubic foot of wood.

EXAMPLE IV Test sticks are impregnated with ammoniacal basic zinc chloride to an equivalent'ZnO retention of 1.5 lbs. Zn() per cubic foot of wood byy the empty cell procedure as in Example I, and then after partial drying, with a 33% zinc chloride solutionv bythe full cell procedure When ammonia gas. is used, it should be. added.

9. as in Example L The sticks are leached 15 days and the excess of zinc chloride is removed. Part remains undissolved and combines with the basic zinc chloride. The following table shows the amounts of zinc, calculated as ZnO, and of chlorine, retained by the wood, and also the tire tube loss, after 15 days leaching. i

t ZnO Lbs/Cu. Ft. Added Percent Fire Tube As- Loss Cl Total Total Lbs/Cu. Ammoniacal Zinc Ft. ASTM Basle Zinc Chloride 3 Min. Final Chloride These results areexcellent for only 2.8 lbs. ZnO per cubic foot.

The mechanism of the treatment of this example i thought to be as follows: the zinc chloride reacts with the residual ammonia to form zinc hydroxide, which reacts with more zinc chloride to form basic zinc chloride. Residual zinc oxide, hydroxide, and`very basic zinc chloride react with added zinc chloride toform basic zinc chloride with a basicity, for example, of one or two to one. EXAMPLE V Fifteen test sticks are divided into three groups of tive, designated A, B, and C.v The sticks of groupA are treated witha water solution of chromated zinc chloride containing 30% chromated zinc chloride by weight, by

the empty cell procedure as in Example I. The sticks in' this group (A) are air dried at 40 C. The sticks of groups B and C are impregnated, together, with the 30% chromated zinc chloride water solution by the same procedure. i The' sticks of groups B and C are subsequently treated with aqua ammonia containing about ammonia by weight, in an amount of solution sufficient to contain an excess of the quantity of ammonia required to combine with all the chlorine as determined by the amount of chromated zinc'chloride retained.- The sticks in group B are air dried at 40 C. 'The sticks in group C are dried at 80 C. The following table indicates the results obtained.

The results show that the treatment with basic material improves chromated zinc chloride as it does ordinary zinc chloride. However, the tire resistance is probably lowered somewhat by the chromium.

Examples of mixed treating solutions which have given satisfactory results are as follows:

Amounts Used-Lbs./Cu. Percent Fire Tube Ft. Wood Loss After Days Leaohing .l

Chromated j Zinc Chloride NH!l 3 Mln. ASTM Calc. as ZnO/ Final Cu. Ft. Wood A 5. 4 none 25 66 5. 2 2. 5 19 30 5. 1 2. 16 31 In the first solution, the water is indicated as being'.

slightly. acidiiied. This is accomplished by adding hydrochloric acid until the pH is approximately 4 5. The

acidification is to prevent incipient Aprecipitation of mag-` nesium ammonium phosphate.

When wood is treated with zinc chloride solution, and

then an alkylene oxide solution is allowed to diffuse into the Wood (or the Wood with the unremoved zinc chloride solution in it is exposed to an atmosphere of ethylene oxide gas) the diiiiculties of high pH are avoided. Ethylene oxide is more expensive than the common alkalis andthe latter will therefore be preferred in many cases for commercial use.

In commercial practice, for wood for external use, it is desirable to incorporate from four to six pounds of zinc impregnant, calculated as pounds of zinc oxide per cubic foot of wood. The treated wood has the desirable pH of around six which tends" to give the wood an even longer life than untreated wood.

The treated wood has high stability to hot water and steam, as a result of which it is particularly adapted to use in cooling towers and wooden hot water tanks.

The basic zinc chlorides of this invention affect the wood as if they were deposited along the walls of the pores in the wood. Although the basic zinc chlorides are not very hard, they tend to rigidify the wood, as shown by 'indentation tests of the wood, but the treated wood saws and handles Well on high speed equipment. The zinc of the basic zinc chloride in the wood treated in accordance with the process of this invention neither leaches nor vaporizes from the Wood. The treated wood is lire resistant, resistant to fungi, toxis yto termites, and repugnant to marine borers. Even barnacles adhere to it to a lesser degree than to untreated wood.

Although this invention as applied to'wood is intended primarily for iire resistant wood where considerable amounts of zinc are used, the process is also useful for window sash and all those applications where toxicity to lated as ZnO is effective.

basic chloride, we prefer it where tire resistance is of secondary importance.

As is levident from the examples, a more highly concentrated solution of zinc salt is generally used in the empty cell process than in the full cell process, For various special applications such as the window sash' mentioned above, the concentration used in either process.-

may be varied over wide ranges.

In the case of wood, the introduction of the solublel zinc salt as the second step of the process has the advantage, when the lirst reactant is an aqueous 'solution of vaporized propylene @common base, of insuring that` there is an excess of "theY water soluble zinc salt, since, aftery removal of thev free liquid, the amount of base present is limitedf. This, in turn, insures that the: pH of the treated wood will be; uniformly low, whereas when the stron-gv base is intro.- duced second, there is some dangerof the formation of localized hot spots of highvpH. This latter danger can be minimized by controlling the conditions of treatment, butv 'it can be eliminated by using the base-soluble salt sequenceof steps.-

`Ina thetreatment vof -fa-bric, as hasl been pointed out above, theV fabric is invariably first impregnated with asolutionof the water soluble zincy salt.

In comparing the re resistance: of fabrics in the eX- amples which follow, a strip of fabric one inch wide and six; inchesv long is prepared. A Mekker-type gas burner is adjustedv to produce a flame aboutl 11/2y inches high. The strip is then suspended from one of its narrow ends so that the lower end just touches the tip of the flame. The cloth is maintained in that position until it has ignited, or,A if'it will not flame, until the char glows. The piece is ratedY as follows:

E-No flaming G-Flaming but selfextinguishiug F-Slow flame spread over all the cloth PV-Rapid flame spread solvents such as ethyl alcohol may be used-in whole or in part inv place of the water.

The fabric to be treated has preferably not been previously treated by any other processes. If the. fabric has been sized or otherwise rendered somewhat non:- absorbent, the fabric should be rendered absorbent by thel removal of the size or other such material.

The fabric is impregnated with the zinc salt solution,

either by immersing the fabric. in the solution or by sprayingy or otherwise applying the solution. to the fabric. Afterl sufficient of the solution has beenv absorbed, any free liquid is removed from the fabric by rollers or any other suitable means. The fabric may then be air dried to remove a part of the remaining solvent. The amount of drying required is related tothe concentration of the solution. Such air drying is possible, without` damage. to the fabric, because the solution isfnot strongly acidic. An alcoholic solution may dry more quickly. than an aqueous one. Thisv drying tends toV make the treated cloth, more resistant to laundering and to. minimize any tendency to dusting. While the theory of its operation. forms no part ofthis invention, it is thought that during this drying process, some of the zinc salts migratev from the outside ofthe fibers to the interior of the fibers.

The, s econd step of the4 process ofV this invention. as. applieclto fabric, is the supplying, at the site of the. Water-soluble zinc salt in the fabric, of a reactant in such a form as toy accomplish no substantialfleachingI or other dislodgernent of the water-soluble zinc. salt. This secondV step. may be accomplished in any of several different ways. One way is to expose fabric from whichl thewexcess of water-soluble zinc salt solution has been removed, to an alkaline gas such as ammoni-a or an amine, suchforexample, as monomethylamine.

Another Way is to expose the damp-dried cloth -to av gaseousy alkylene oxide, such as ethylene O Xidc,` or

oxide, epichlorhydrin, butylene oxides, arylalkyl oxides, cyclo-alkyl oxides, and polyepoxy compounds.V

Another way is to dissolve a basic material such as mixed` ammoniai or' ethylene oxideV in an organic solvent in.-

which the water-soluble zinc salt is insoluble; and spray theV damp-dried. cloth with or dip it in the organic.,

depositing of a basic zinc salt in place in and on the` fibers of the fabric. In the case of the initiall impregnation of the. fabric; withl an alkyleneoxide dissolved in anhydrous ethyl alcohol along with- Zinc chloride, with theV subsequent supplyingy with moisture, or the exposure of the damp'zine chloride` impregnated, fabric to alkylene oxide gas, thereaction maybe exemplified by the followf ing equation: (n+1)ZnC12+2n(CH2)2o+2nH2o= ZnC12 nZn OH 2+ 2n CH2 OHCI 'When an alkaline gas is used, the reaction may: be, exemplified by they following equation:

ZnC12 nZnO'l-Ig -1- 2nNH4Cl When thev third step. is complete, the cloth contains the basic; zinc salt as an insoluble compound, and. in

addition' will, contain soluble inorganic salts or organic The cloth can be freed:k

compounds` such as chlorhydrin.

of' these materials by rinsing in water. The cloth is then dried. Organic materials. including chlorhydrin can also be removed by evaporation on heating.

The following examples are illustrative of the process of this invention as applied. to` fabric.

EXAMPLE IX' A piece of five ounce cotton twill was washed to remove any size, and thoroughly dried. It was then soakedV in a solution containing 4.0% zinc chloride and 60% water by weight, for 30y minutes at room temperature. The cloth was removed from the solution and the excess liquid removed from the cloth by a rollertype wringen at which time the cloth contained solution in the. amount of 200% of its dry weight, hereafter referred to as a 200% Wet pick-up. The cloth was then dried until the Weight was reduced C50-35%. This treatment constitutes the iirst step in the process.

This cloth Was then put in a covered container containing an amount of ethylene oxide equal. to 3 mols of ethylene oxide for each mol of zinc chloride contained in the cloth, as calculated from the amount of retained l solution., The. impregnated cloth was left in the con-v tainer in contact with the gaseous ethylene oxide; for a period of 1 5 to. 2,0 hours. The cloth was then remQved from the jar `and air driedl at 70 C.,

The following table indicates the results obtained: I

In each washing cycle the cloth was washed for l0 minutes in a .5% detergent solution at 30 C. in an agitator-type washing machine; rinsed in tap water at` 40 C.; dewatered and driedA at 70 C. The detergentl 13! used was Orvus Extra Granules, a Procter and Gamble product.. Similar results were obtained with the following detergent:

. Percent Tall oil-ethylene oxide compounds (Armours ynonionic Ethofat 242-25) .29 Sodium tripolyphosphate 68 Low viscosity carboxymethylcellulose a.. a v3 Total 100 It is of interest to note that the addition of copperv chloride, CuCl2, to either the fabric or wood treating solutions produces, in the ethylene oxide treatment, a green colored fungicidal impregnant.

The treated cloth is dust free, in the sense that no cloud of dust appears, on tearing. It is believed that the ethylene oxide and the chlorhydrin which is formed in the process of reacting with the zinc chloride may react together or with the cellulose to tie the basic zinc chloride formed to the tibers.

The strength of the cloth after the treatment is often as much as 30% or more greater than itsstrength befor treatment.

IEXAMPLE X A piece of five ounce cotton twill was treated with zinc chloridesolutionin the same manner as the cloth in Ex- 14 chlorine content of the cloth are indicated'in the following table:

Fire resist- Percent Percent ance Zn Cl glotll; after insing E 24. 9 5. 6 ot eter was Cloth after 3 washes F-l- 20. 1 2. 3

The dusting of the cloth was moderate after rinsing and slight after three washes.

EXAMPLE XII A piece of five ounce cotton twill'was treated with the zinc chloride solution of the same strength and in the same manner as in the first step of Example IX, except Fire resist- Percent Percent ance Zn Cl Cloth after rinse E- 19.6 4. 3 Cloth after 1 Wash E Cloth after 3 washes G- 18. 9 3. 2

ample I.` The cloth, from which the excess liquid was removed as in Example I,'was placed on a rotating supportv in acovered container. The solution retained by the cloth contained a calculated 46 grams of zinc chloride. One hundred grams of ammonia, in the formof 26% aqua ammonia was placed in the bottom of the container.` The cloth was kept out of contact with the ammonia solution, but was exposed to the evolved gas. The cloth was exposed tothe ammonia gas for 45 minutes, removed from the container, air dried at room temperature, and then further dried at 70 C. to constant dryness. The following table indicates the results obtained:

Fire resist- Percent Percent ance Zn Cl Cloth after rinsing 22. 2 5. 7 Cloth after 1 wash---" E Cloth after 5 washes F 17. 9 1. 6

EXAMPLE XI A piece of four ounce viscose rayon cloth was treated with a zinc chloride solution as in the first step of Example IX.

,The cloth was then put into a coveredl container with two mols of ethylene oxide for each mol of zinc chloride.

The ethyleneloxide gas was permitted toco-ntact the cloth as in Example 1X. The cloth was then removed from the container and, without drying, was rinsed and then dried at 70 C. The fire vresistance and z inc and which have been place of the epi- The various other alkylene oxides suggested heretofore may be used in chlorhydrin of Example XII.

EXAMPLE XIII A, B and C were washed and dried. Piece A was soaked in a water solution containing 15% zinc chloride. Piece B was soaked in a water solution containing 25% zinc chloride, and piece C was soaked in a water solution containing 3`5% zinc chloride. The soaking time for each of the pieces was 30 minutes, at room temperature. At the end of 30 minutes, the pieceswere removed from their respective solutions and the excess liquid expressed to give a 200% Wet pick-up. The pieces were dried at 70 C. for five to ten minutes. The weight losses on drying were 55% for piece A, 50% for piece B, and 40% for piece C. The pieces were put into closed containers with 3 mols of ethylene oxide per mol of zinc chloride. The pieces were allowed to remain in contact with the gaseous ethylene oxide for a period of six hours. They were then removed from the container and dried at 70 C. They were' then rinsed in clear water and again dried. The three pieces were washed at 60 C. using a detergent as in Example I. The following table The results shown by the table indicate that within the range of amounts of zinc used in treating pieces A,

B and C, the larger theamount of zinc retained, the better the lire resistance of the cloth, and the more permanent the fire resistance with repeated washing.

asesor/'s The. chlorine loss. before rinsing appears to be the result of the chlorines becoming part of an organic molecule which is volatilized.

In carrying out the treatment of cloth using ethylene oxide, the ethylene oxide cost may be reduced by recovering any excess ethylene oxide and reacting any volatilized chlorhydrin with sodium hydroxide orV calcium hydroxide to regenerate the ethylene oxide. O ther Vreaction byproducts can also be recovered.

EXAMPLE XIV Two pieces of ve ounce cotton twill, identified as A and B, were treated with a water solution containing` 60% zinc chloride to an increase in weight of 140%. The two pieces were then placed' in a closed container containing 2 mols of gaseous ethylene oxide per mol' of' zinc chloride in the cloth, for 18 hours. The pieceswere then removed. Piece A was heated to 90-100 C. for 12 hours and then rinsed. Piece B Was rinsed without heating. In both cases the basicity of the irnpregnant in the rinsed cl'oth was approximately ZnCl2-4Zn(OII-)2. Approximately 4% of the initial zinc in piece A was dissolved in the rinsewater.

Approximately 60% of the chlorine was driven off during the heating of piece A, presumably as chlorhydrin. This accounted for 37% of the added ethylene oxide. Approximately, 8% of the chlorine was leached as chlorhydrin, and 5% as ionic chlorine during the rinsing process. The remaining chlorine was retained by the cloth, so that all of the chlorine was accounted for. Approximately 13%- of the added ethylene oxide was not reacted. The ethylene oxide balance with respect to piece A is as follows:-

Percent Unreacted 13 Volatilized as chlorhydrin 37 Rinsed as chlorhydrin 8 Unaccounted 42 The cloth contained only basic zinc chloride. The unaccounted ethylene oxide must therefore have been volatilized and leached as ethylene glycol or complexes based on lthis material.

Piece B gave similar results, with the chlorhydrin being leached upon rinsing. All of the zinc and chlorine were accounted for. The unaccounted ethylene oxide was 36%.

The. treated cloth showed good iire resistance and hand.

EXAMPLE XV Stock was obtained by disintegrating tilter paper in water. 36.5' grams of paper pulp was slurried in- 2000 grams of a water solution containing 15% zinc chloride. TheI pulp was then ltered to reform the paper. It was sucked dry and pressed. Two sheets were formed, one approximately lAS inch thick, the other approximately 1;@ inch thick. The sheets of paper were placed in a closed container with 3 mols of ethylene oxide per mol of zinc chloride retained in the paper, for 16 hours, at room temperature. The t-hick piece of paper showed a re resistance of E and the thin piece of paper showed a iire resistance of F, which illustrates the difficulty of tire-proofing thin materials. The paper analyzed 13.6% zincand 3.1% chlorine.

Paper similarly treated with zinc chloride in pulp form i t6 EXAMPLE XVI A piece of wet strength paper toweling (Scott Paper Co.) was soaked in a water solution containing 50% zinc chloride and dewatered to 200% pick-up. It was then vplaced in a covered container with 2 mols. of gaseous ethylene oxide per mol ofl zinc chloride retainedY bythe paper toweling, for 16 hours, at room temperature. The paper was then dried at C. Its tire resistance was E. The paper analyzed 31.6% zinc and 7.6% chlorine. After rinsing and redrying at 70 C., the iire resistance was still E.A After washing at 60 C., in an agitator-type Washing machine with a .5% detergent solution as in Example I, the lire resistance was G-.

The treated paper was noticeably whiter and more opaque than the original paper. The tear resistance ot the treated paper appeared' to be superior to that of the untreated paper.

EXAMPLE XVII A piece of ve ounce cotton twill was treated with zinc chloride and ethylene oxide as in Example IX. Its analysis, after it had been rinsed and dried, showed 24.9% zinc and 5.6% chlorine. The cloth was then dry cleaned by tumbling, in iive minute cycles, in trichloroethylene solution. Atl the end of each tive minute cycle it was air dried, then covered with a moistenedy cloth and pressed dry with a hot iron. After twenty cleaning cycles, the cloth hada re resistance of E. It analyzed 21.3% zinc and 5.3% chlorine, which shows that organic solutions such as those used in dry cleaning do not remove the basic zinc chloride.

EXAMPLE XVIII A piece of ve ounce cotton twill treated with zinc chloride as in the irst step in Example IX was placed in a solution of ammonia in trichloroethylene. The amount of ammonia in the trichloroethylene solution was, in the proportion of 2 mols of ammonia to 1 mol of zinc chloride contained in the cloth. After 20 hours at room temperature, the cloth was removed, dried, and rinsed. The cloth analyzed 15.6% zinc and 14.1%v chlorine. Its re resistance after rinsing was E. i

EXAMPLE XIX A piece of five ounce cotton twill was treated with zinc chloride solution as in the rst step of Example IX, and.

then placed in a solution of ethylene oxide in trichloroethylene. The ethylene oxide dissolved was equivalent to 2 mols of ethylene oxide to one of zinc chloride in the cloth. The cloth was removed from the solution after 20 hours, air dried, rinsed, and dried again. The cloth analyzed 20.7% of zinc and 4.0% chlorine and showed a tire resistance after rinsing of E. After a wash in a .5% detergent solution as in Example I, at 60 C., the lire resistance was E. A two hour period ofY exposure to the ethylene oxide produced acloth containing 13.1% zinc` and 2.7% chlorine.

EXAMPLE XX A piece of iive ounce cotton twill was soaked in a water solution containing 30% zinc chloride and 10% magnesium chloride for 15 minutes at 25-30 C. The excess of water was removed to give 200% pick-up. The pierce was placed in a covered container and exposed to the equivalent of 2 mols of ethylene oxide per mol of zinc chloride, for 16 hours at room temperature. The

l cloth was thenair dried for 10 minutes and subsequently oven dried for 30 minutes at 70 C. The cloth analyzed 4.5% magnesium, 7.0% zinc, and 9.2% chlorine. The fire resistance of the cloth was E, but its resistance to washing was poor.

It may be observed from the examples that the re 17 resistance of the fabric and permanenceof the treatment are not altogetherdependent upon .the amounts of zinc and chlorine retained by the fabric, but are also dependent upon the mannerin which the fabric is impregnated.

The optimum amount of retained zinc for cloth which is to remain soft is,15-,25%. inl order to obtain this range, approximately a 200% Wet pick-up of 40% zinc chloride L,solution is desirable, whereas if a 60% Zinc chloride solution is used, a 140% wet .pick-up is satisfactory.

When the concentration of zinc chloride solution exceeds about 65%, the zinc chloride begins to react with cotton cloth to parchmentize or mercerize it. 'At a concentration of 70-75% zinc chloride, the reaction is strong. When this reacted cloth is treated with ethylene oxide, and rinsed, the cloth is stiff and harsh, but its fire resistance is excellent, even after many washings. In treating cellulosic fabric with these highly concentrated solutions of zinc chloride, it may be found desirable to apply the solution hot, so as to reduce the viscosity of the solution, or to spray the cloth and immediately to pass it through rollers, depending upon the amount of parchmentizing and impregnation required. The following example is illustrative of this heavy treatment.

EXAMPLE )OCI A piece of cotton twill was soaked in 75% aqueous zinc chloride solution for 30 minutes at room temperature. The wet pick-up was reduced to approximately 350%. The cloth was treated with 2 mol equivalent of ethylene oxide in a closed container for 16-20 hours.

The cloth was rinsed and dried. It analyzed 34.8% zinc and 9.5% chl-orine. The fire resistance was E.

After washingfZO cycles in 0.5% Orvus Granules at 60 C., the re resistance was E-. The cloth analyzed 32.1% Zinc and 4.0% chlorine.

The uses to which fabric treated in accordance with the process of this invention may be put are manifold. For example, clothing, tents, tarpaulins, curtains, carpets, rope, fishnets, and the like may be rendered fire resistant and cloth and paper, increasingly opaque. Heavy cloth, heavily treated, may be used for Welders curtains and fire Walls of buildings. Such cloth may be suspended over potentially dangerous areas, to be dropped in case of fire to smother the flames. In such applications, the cloth may bey reinforced with glass bers, metallic threads, asbestos fibers or the like.

All pieces of wool cloth impregnated with basic zinc chloride in accordance with this invention, have been markedly intumescent.

Thus it can be seen that a two step process is provided by which a substantially pure deposit of a coprecipitate of zinc hydroxide and a normally water soluble zinc salt is formed in situ in the pores of porous material and in and on the fibers of fibrous material in such a way that the deposit strongly resists leaching or dislodgement, and that the treated materials themselves are unique.

Having thus described the invention, what is claimed and desired to be secured by Letters Patent is:

1. The process of treating cellulosic material comprising irnpregnating the material, in separate steps, with a solution of a water soluble zinc salt and with a reactant which produces, with a portion of said water soluble zinc salt, zinc hydroxide, and co-precipitating the zinc hydroxide and residual water soluble zinc salt, in the form of water-insoluble basic zinc salt, in situ.

2. The process of treating cellulosic material comprising first impregnating the material with a solution of water soluble zinc salt, then impregnating said material with a basic material which produces, with a portion of said water soluble zinc salt, zinc hydroxide, and co-precipitating the zinc hydroxide and residual water soluble zinc salt, in the form of Water insoluble basic zinc salt, in situ.

3. The process of treating a fabric, comprising wetting the fibers of said fabric with an impregnant solution coni8 taining avwater-soluble zinc salt, then thereafter introducing into the impregnated fabric a reactant, in a medium by which the zinc salt is not leached or dislodged, capable of reactingfwith the impregnant to co-precipitate therefrom zinc hydroxide and the said water-soluble Zincsalt, and drying the said fabric.

4. Fabric containing zinc hydroxide and a water-soluble Zinc salt co-precipitated in accordance with the process of claim 3.

5. :The process of claim 3 wherein the reactant is a gaseous substance taken from the group consisting of ammonia and ethylene oxide.

6. The process of claim 3 wherein the reactant is an alkylene oxide.

7. The process of claim 3 wherein free solution is removed frorn the fabric after the fibers of the fabric are wetted, and the reactant is supplied in solution in an organic solvent in which the water-soluble zinc salt is substantially insoluble.

8. The process of claim 3 wherein the solution containing a water-soluble zinc salt also contains yan organic fabric-treating material soluble in the water-soluble zinc salt solution and precipitated from solution with the basic zinc salt.

9. The process of treating wood comprising impregnating the wood with a water-soluble zinc salt taken from the group consisting of Zinc chloride, zinc sulfate, chromated zinc chloride andchromated zinc sulfate, and subsequently impregnating the wood with an amount of a basic material sufficient to co-precipitate zinc hydroxide and the said water soluble Zinc salt in situ in the wood.

l0. The process of treating wood in which there are pores, comprising filling pores of the wood with a concentrated solution of a water-soluble zinc salt taken from the group consisting of zinc chloride, zinc sulfate, chromated zinc chloride and chromated zinc sulfate, at least partly evacuating the said pores of free solution, filling said pores with a basic material, and co-precipitating zinc hydroxide and the said water soluble zinc salt on the walls of said pores.v

ll. The process of treating wood comprising impregnating wood with a basic material, subsequently impregnating the wood with sufficient of a water-soluble zinc salt taken from the group consisting of zinc chloride, zinc sulfate, chromated zinc chloride and chromated zinc sulfate, to co-precipi'tate zinc hydroxide and the said water soluble zinc salt in `situ in the wood and to produce a pH in the impregnated Wood of less than 7.

12. The process of treating wood comprising impregnating the wood with zinc chloride, subsequently impregnating the wood with a solution containing suiicient` ammonia to elo-precipitate zinc hydroxide and the said zinc chloride in situ in the wood.

13. The process of claim l2 wherein the solution of ammonia contains zinc chloride.

14. The process of claim l2 wherein the solution of ammonia contains basic zinc chloride.

l5. The process of treating Wood comprising impregating the wood with zinc sulfate and subsequently impregnating the wood with a basic material yand co-precipitating zinc hydroxide and zinc vsulfate as basic zinc sulfate. n 16. The process of claim 9 wherein the basic material contains an `anion taken from the group consisting of chloride, sulfate, bromide, phosphate, arsenite, arsenate, and berate.

17. The process of treating wood comprising impregnating wood with a solution of zinc chloride, subsequently impregnating the wood with ethylene oxide and precipitating basic zinc chloride in situ in the wood.

18. The process of producing fire resistant wood having low electrical conductivity, comprising leaching the wood with water `to remove water-soluble salts, impregnating the wood with zinc chloride, impregnating the wood with ethylene oxide, precipitating basic zinc chloride in situ `Iinthe wood, drying the wood, and evaporatirtlhg the volatile References Cited in the le of this patent f, reaction products of the zinc chloride and e ylene oxide.

j 19. The process of claim 9 wherein one of the im- UNITED STATES PATENTS .,pregnants contains Ian arsenic compound, which is pre- 831,450 Lowry Sept. 18, 1906 ,cipitated with the basic zinc sulfate. 5 1,318,523 Arent et al Oct. 14, 1919 20. Wood treated in accordance with the process of 1,337,380 Alexander Apr. 20, 1920 claim 18, having low electrical conductivity, from which 1,846,185 Cline et al Feb. 23, 1932 Vwater-soluble salts have been leached, which contains 2,097,509 Boller Nov. 2, 1937 practically pure basic zinc chloride and which has a pH 2,637,691 Pershall May 5, 1953 of less than 7. l0 2,769,730 Sak Ombut Nov. 6, 1956 

1. THE PROCESS OF TREATING CELLULOSIC MATERIAL COMPRISING IMPREGNATING THE MATERIAL, IN SEPARATE STEPS, WITH A SOLUTION OF A WATER SOLUBLE ZINC SALT AND WITH A REACTANT WHICH PRODUCES, WITH A PORTION OF SAID WATER SOLUBLE ZINC SALT, ZINC HYDROXIDE, AND CO-PRECIPITATING THE ZINC HYDROXIDE AND RESIDUAL WATER SOLUBLE ZINC SALT, IN THE FORM OF WATER-INSOLUBLE BASIC ZINC SALT, IN SITU. 